While hematopoietic stem cells have significant therapeutic potential, a limitation that has hindered their use in the clinic has been the difficulty associated with obtaining sufficient numbers of these cells. In particular, hematopoietic stem cells are resistant to maintenance, propagation, and expansion ex vivo. Another challenge to be overcome in order to further develop the use of hematopoietic stem cells (HSCs) as a therapeutic modality is the loss of multi-potency that can occur when these cells are cultured ex vivo. There is currently a need for compositions and methods for the ex vivo maintenance, propagation, and expansion of HSCs that preserve the multi-potency and hematopoietic functionality of these cells. Described herein is the inventors' discovery of a number of compounds that permit hematopoietic stem cell ex vivo maintenance, propagation, expansion and enrichment. The compositions and methods of the invention address the challenges posed by conventional HSC therapies by providing strategies for maintaining, propagating and expanding these cells and also enriching heterogeneous cell populations with HSCs while preserving the ability of the ex vivo cultured cells to self-renew and differentiate into a multitude of different blood cell types both in vitro and upon transplantation into a recipient.